A metal film has been recently of increasing interest, because of restriction of the use of lead in electronic part circuits, needs of metal film patterns in low-resistance metal wiring, a printed circuit board (PCB), a flexible printed circuit board (FPC), an antenna for a radio frequency identification (RFID) stag, and electromagnetic shielding, and new fields such as a plasma display panel (PDP), a thin film transistor-liquid crystal display (TFT-LCD), an organic light emitting diode (OLED), a flexible display, an organic thin-film transistor (OTFT), and the like, and usefulness in simply forming electrodes.
According to a general method, a metal film is formed by depositing or sputtering metal or spin-coating ink containing metal to form a metal layer, performing a photo-resist process through exposure and development to form a desired pattern, and then performing etching to manufacture the metal film indirectly. However, the above method requires complex processing and is not suitable for forming multi-layered patterns. Furthermore, the above method has problems in that development of vacuum deposition equipment is limited due to increase in size of substrate and unnecessary materials generated at the time of forming patterns cause environmental pollution.
Recently, in order to overcome these problems, Japanese Patent Laid-Open Publication No. 2004-221006 (2004 Aug. 5) and No. 2004-273205 (2004 Sep. 30) disclose that nanoparticles, powder or flake of metal, a binder resin or a solvent are used to prepare a paste of metal, or Chem Mater, 15, 2208(2003), Japanese Patent Laid-Open Publication No. Hei 11-319538, Japanese Patent Laid-Open Publication No. Hei 2004-256757, and U.S. Pat. No. 4,762,560 disclose that a metal compound such as silver nitrate, hydrogen tetrachloroaurate, or copper sulfate, reacts with other compounds in an aqueous solution or an organic solvent to form colloids or nanoparticles. However, these methods are limited in the use of various kinds of substrates since they bring about high manufacturing costs and decrease in stability and require a complex process and high firing temperature. In addition, Korean Patent No. 2005-0061285 discloses a method for forming a metal pattern by forming a potential pattern on a substrate using a photocatalytic compound and then performing plating using a desirable metal. However, this method has a short activation time of the potential pattern and is inappropriate in continuous processes.
In order to solve the above disadvantages, a heat compresing process is performed after forming metal patterns. For example, Korean Patent No. 2002-0081822 describes a method of firing metal printing patterns through heat treatment and then performing a heat compressing process. However, this method still has a problem in that there is a limit to densify a metal structure in forming of a metal film.